Would old bulbs cause STN'ing?

[Tigé21v]

My tank is lit with 2x250w XM 20k's running on CoralVue ballasts (7hours) and a 110w VHO Super Actinic/454 combo (14 hours).
I've had a couple of my acros starting to STN at the very tips. Started a couple of weeks ago with a purple, and has now moved to the blues also.
However, the pieces I have in a frag tank, (including a purple), seem to be fine. The frag tank is tied to the display tank, so same water. There's been no changes or swings to the system.
The XM bulbs are a little over a year old. Could old MH bulbs be causing this?

 

[flyyyguy]

not if they are only that old

however, soemtimes many things can be the straw that broke the camels back. If there are other factors that are contributing to poor coral health, less than ideal lighting certainly sint going to help. But again, not only being a few months past when they should be changed

 

[Tigé21v]

Then I don't have a clue what's going on in my tank. I'll retest all parameters when I get home this afternoon.
After thinking about it, here are two tings I've done over the past month, though I wouldn't think either one would have a negative effect.
I've been working in a bucket of Reef Crystals someone gave me. (I use Kent). But I've only been adding about 20-25% of the RC to the Kent at a time.
The other thing I did was upgrade my RO unit. I ws using a 5 micron sediment and 5 micron carbon block, and BRS DI resin. I added a 1 micron block after the 5 micron, and switched the BRS DI resin over to Spectrapure MaxCap 2-stage DI resin.
Would either one of these possibly be the source of the problem?

 

[Ron Popeil]

in my experience, burnt tips is the result of an alkalinity change or phosphate issue.

i know you said nothing has changed water parameter wise, but maybe you should double check your alkalinity with another alk test kit just to be sure yours is still accurate.

same for phosphates.

how old is your ballast powering your halide bulbs?

 

[chuckreef]

Reef crystals does have a higher alk than most salt mixes.
That might/could be just enough to shock the tips.
I still don't understand the word "burn" in the commonly used phrase.